Vascular reocclusion remains a significant complication of stent placement: vascular reocclusion occurs in 30-50% of subjects within 1 year of vascular surgery. In-stent restenosis is due primarily to neointima hyperplasia of smooth muscle cells. Thus, understanding the mechanism(s) and biochemical participants in neointima hyperplasia will optimize the design of intervention protocols that reduce the risk of restenosis after vascular surgery. Our Preliminary Results suggest that apolipoprotein (apo) J / clusterin may be an important regulator in determining the vascular response to injury and the development of the neointima lesion. With genetically defined mice as the model, our results show that apoJ expression is induced in response to mechanical injury of the carotid artery. Importantly, apoJ(-/-) mice developed a more severe neointima lesion 2 wk after arterial injury in comparison to wild type mice. Moreover, additional Preliminary Results demonstrate that apoJ(-/-) mice develop increased hypercholesterolemia compared to apoJ wild type mice fed the same cholesterol enriched atherogenic diet. This hypercholesterolemia is associated with an altered distribution of apoE among lipoprotein particles. Therefore, the current study uses the in vivo mouse model to test the hypothesis that apoJ has a direct vascular protective function in vivo by modulating one or more of the cardinal events that contribute to vascular occlusive disease. Specific Aim 1 contains three parts. First, the sequence of events from the time of vascular injury to the time of neointima formation in wild type and apoJ(-/-) mice is compared. The time when differences in vascular pathology are observed is correlated with the temporal expression of apoJ in wild type mice. With these data as a guide, the second part performs gene expression profiling studies to determine the biologic and functional pathways that are modulated by apoJ in the vascular response to injury. The third part uses apoJ-tg mice and adenovirus mediated apoJ gene transfer directly to the vessel wall to test the corollary hypothesis that increased apoJ expression is a viable tactic to limit neointirna hyperplasia. Specific Aim 2 tests the hypothesis that apoJ deficiency exacerbates diet induced hypercholesterolemia by decreasing lipoprotein catabolism via alteration of apoE distribution among lipoproteins. We will characterize the metabolism of VLDL particles in apoJ wild type and apoJ(-/-) mice: quantify catabolism, quantify lipoprotein synthesis and secretion, and quantify transter of apoE from HDL to VLDL. In Specific Aim 3 wild type, apoJ(-/-), and apoJ-tg mice are fed a cholesterol enriched atherogenic diet to test the hypothesis that apoJ is protective, also, against progressive atherosclerosis. Taken together, these studies will identify novel functions of apoJ as well as contribute to our better understanding of the pathogenic events in the vascular response to injury.